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Working on my Nintendo Kirby alternate universe where things are more biologically realistic.

Many life forms are roundish legless creatures that can move by bouncing. How can this work and is it as efficient as legs?

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    $\begingroup$ Spoiler: There is no vehicle or mode of transportation that exists (except in the rare cases of gimmick vehicles) which is propelled via bouncing. It will not be as efficient as legs. $\endgroup$
    – Halfthawed
    May 21, 2020 at 4:14
  • $\begingroup$ @Halfthawed well to be fair their are leg based modes of transport based on bouncing. $\endgroup$
    – John
    May 21, 2020 at 4:37
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    $\begingroup$ the problem is any form of bouncing can be made more efficiency with any projection ,making legs inevitable. you also have to be generating a lot of force to bounce, so you have to think of why a creature would be able to generate such force without limbs. $\endgroup$
    – John
    May 21, 2020 at 4:38
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    $\begingroup$ Maybe symbiotic relationship with other intelligent species that would paste a post-it note label "kick me"... $\endgroup$
    – user6760
    May 21, 2020 at 10:30
  • $\begingroup$ Or it gets carried around by August Strindberg. $\endgroup$
    – user535733
    May 21, 2020 at 19:16

3 Answers 3

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Give them a hydrostatic skeleton.

Earthworms are roundish, legless creatures. They don't happen to move by bouncing, but they get along quite well without any bones or joints. How?

They have cavities inside their bodies that are filled with incompressible fluid, and muscles wrapped around those cavities in different directions. Flex one set of muscles, and because the fluid is not compressible, the cavity is forced to elongate. Flex a different set of muscles, running perpendicular to the first set, and the cavity contracts.

In the case of movement by bouncing, you'd need the muscles be fast enough and strong enough that the mere inertia of the fluid in the cavity when it's being elongated (presumably "upwards", perpendicular to the ground) is enough to lift the creature off the ground for a moment. But the concept is there.

(Can this be as efficient as legs? That's above my pay grade, I'm afraid--although the apparent lack of existing organisms that travel by bouncing might leave a clue...)

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First of all, They would need some way of initiating motion. At the very least, they might need a scaly sort of skin such as snakes use to start moving. OK, now they are rolling. If they are flexible, then they could move some muscles to effectively "jump" by pushing off from the current contact area. Then, as comments suggest, a series of jumps as kangaroos and various rodents use would be fast if not energy-efficient.

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These creatures could be structured similar to a primitive nephrozoon balanced on its tail, but short and round. It would jump by rapidly extending its body, and could change direction by leaning in the direction they want to go before jumping.

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